In the blow molding of plastic jugs or other handled ware or of structural shapes having reinforcing ribs or the like, substantial difficulty has been involved in providing pinched-shut, non-blown portions of the blown article. For example, in the manufacture of handled articles, the hand hole in the final article is formed by pinching shut a portion of the blowable shape prior to the inflation of the shape interiorly of a closable blow mold. Generally, the blow mold sections are closed into a blowable shape which has been previously "puffed" or radially distended by the injection of a limited volume of air to increase the size of the initial parison to an extent such that the blowable shape can be pinched shut by the blow mold, as in U.S. Pat. No. 3,389,424. Alternatively, the blowable shape may be a blown pre-form, as proposed in U.S. Pat. Nos. 3,740,181 and 3,781,395 assigned to the assignee of the present invention.
In either event, the blowable shape is of sufficient size to encompass the non-blown portion, e.g. the hand hole, of the final container and at least a part of the surrounding blown portions, .e.g. the handle, of the container. This blowable shape is then interposed between a pair of closable blow mold sections, and the mold sections are closed upon the blowable shape to pinch it shut, particularly in the hand-hole area. More, specifically as the blow mold sections close onto the blowable shape, the blowable shape is engaged by pinching projections on each blow mold sections, and these pinching projections pinch shut the periphery of the hand hole opening, so that the material filling the opening will not be blown during subsequent inflation of the blowble shape interiorly of the closed blow mold sections.
During closure of the blow mold sections, any relative movement between the blowable shape and the blow mold sections will upset the material distribution within the final article and any shape-mold misalignment results in a poorly made article. Further, the contact between the blow mold projections and the blowable shape tends to freeze the blowable shape to an extent such that final welding shut of the pinched portion may not occur upon full mold closure. Any failure to weld shut, particularly in fast setting materials, such as polyvinylchloride, will result in a non-sealed container which must be scrapped.
All in all, severe production problems have been encountered in the past in the blow molding of blown articles having pinched-shut, non-blown portions. Such problems include (1) poor material distribution in the final article, (2) relative movement and misalignment between the blowable shape and the blow mold sections, resulting in excessive scrap or inadequate material to form the final article, (3) excessive chilling of the blowable shape prior to full mold closure and blowing, resulting in welding failures, and (4) difficulties in blow molding fast setting materials, such as polyvinylchloride.